The present invention relates to devices for treating fluids, such as water, and more particularly, to fluid treatment devices which are powered to provide electrical and magnetic fields in the fluid.
Fluid treatment with DC-powered solenoid coils has been used for many years. Such an arrangement is shown in U.S. Pat. No. 4,938,875. The DC power can be provided by a DC source (battery) or a rectified AC source. For example, U.S. Pat. Nos. 5,702,600; 6,063,287 and 6,146,526 have modified the AC method by using only a rectified half-wave to generate the DC power (without a smoothing power capacitor) and letting the coils ring with the current closed off for the second half wave. During the no-current period, the coils will ring at their resonant frequency (which can be modified by the addition of a small amount of capacitance) and emit a high frequency field into the fluid to be treated. In the '600 patent, a diode is used to rectify the wave and in the '287 patent, a triode is used to rectify the wave. The coils are energized at a line frequency of 50 or 60 Hz, and not at a natural resonant frequency of the coil or the circuit.
U.S. Pat. No. 5,725,778 discloses the use of a square wave generator with either a fixed frequency (500 Hz) or a sweep frequency (1 KHz to 3 KHz), neither of which is at the natural resonant frequency of the coil or the circuit.
Exciting or pulsing a coil at its resonant frequency, or the resonant frequency of the LC circuit it is a part of, is known, particularly in the field of inductive heating, and an exemplary patent using this arrangement is U.S. Pat. No. 3,958,883.